1. Field of the Invention
This invention relates to folding agricultural implements, and in particular to a frame for a forwardly folding implement having a tongue which extends rearwardly during folding such that the weight of the implement remains supported primarily by wheels of the implement and is not unduly shifted to the tractor drawbar.
2. Description of the Related Art
Agricultural implements, such as planters, drills, cultivators, fertilizer applicators and the like are often built on a frame which is designed to fold up for road transport and to unfold for field use. One common type of folding implement frame is known as a forward folding frame. Forward folding frames typically comprise a longitudinal tongue and left and right wings pivotally connected to the tongue. The wings are moveable between a field position wherein the wing are generally perpendicular to the tongue and a transport position wherein the wings extend forwardly and are oriented generally parallel to the tongue. In such a design, the tongue must provide a sufficient distance between the wing pivots and the rear of the tractor for the wings to be able to move into their forwardly extended position without hitting the tractor.
If the tongue were of a fixed length, an implement of a practical width would be excessively long and awkward to turn in the field, therefore forwardly folding implement frames have typically been provided with telescoping tongues which extend as the implement folds. For example, U.S. Pat. No. 5,113,956 to Friesen et al. discloses a forwardly folding implement frame having a telescoping tongue which extends forwardly as the implement folds in order to provide sufficient clearance for the wings. A problem with forwardly extending tongues of this type is that, as the tongue extends, the wheels supporting the implement are pushed rearwardly, away from the tractor. This causes the weight of the implement to shifted from the supporting wheels to the tractor drawbar. Excessive weight on the tractor drawbar can cause damage to the tractor or cause the front of the tractor to tend to lift, making it unstable. An implement of this type can also be difficult to unhitch from the tractor since the large percentage of its weight resting on the drawbar must be lifted with a jack during the unhitching procedure.
A previous attempt to address this problem is disclosed by U.S. Pat. No. 5,488,996 to Barry et al. This design uses a forwardly extending tongue like the one taught by Friesen et al. '956 but mounts the supporting wheels on a slidable carriage which moves forward as the tongue extends. The forward movement of the wheel carriage reduces the down load on the tractor when the implement is in the transport position, however it appears that the majority of the weight of the implement is still carried by the drawbar.